Metal machining and drilling bits

ABSTRACT

The drill ( 20 ) include a shear off safety feature. The flats ( 21 ) are connected to the bit ( 22 ) via a wasted section ( 23 ) so that upon jamming of the bit in a workpiece the wasted section will twist and shear off releasing the operator. The shank of the bit is made long enough that even if it is sheared there is still enough shank so that the but may still be used to complete a drilling procedure if this be required. The shear torque is typically 15-30 ft lbs. Preferably 15-20 ft lbs for domestic drills and 20-30 ft lbs for industrial drills.

TECHNICAL FIELD OF THE INVENTION

THIS invention concerns twist drills, router bits and like componentswhich are normally held in three jaw chucks.

BACKGROUND TO THE INVENTION

For both machining work and jobbing work the shanks of such bits arecylindrical and they rely on the operator tightening the chuck jaws togrip the shank firmly enough to impart the necessary torque. Whenunexpected hardness in the substrate is met, the bit may bind in thebore slowing the bit while the chuck may continue to spin. Thisinterrupts the drilling operation and damages the bit.

Tradesmen commonly dispense with the chuck key when tightening a bit inthe chuck, preferring to insert the required bit and then to grip thechuck briefly as it starts, using the torque of the drill to tighten thechuck. This helps to change bits quickly but chuck slip is common withsuch practice.

Spade bits have a single flat ground into the end 10 mm of the shank,but to improve grip this is intended to be placed adjacent a chuck jawso that one jaw will close parallel to the flat.

Other drill bits are known that employ flats along the drill shank.

WO 02/064295 describes in combination a mounting portion of tool and acorresponding shank, the mounting portion of the holder has aball-detent and the shank has a corresponding a circumferential groovewhere the circumferential groove is closely spaced from the insert endof the shank.

U.S. Pat. No. 5,466,100 describes a drill bit having a steppedconstruction, referred to as a cone drill, and a quick change capabilityprovided by a shank having a non-circular cross-section and acircumferential groove for quick connect-disconnect in a power tool ordrill. The cone drill has a circumferential groove close to the end ofthis is used as a reference point to enable an operator to select theparticular hole diameter being drilled.

However, all these known bits are prone to jam and hence create a safetyrisk for an operator. It is an object of the present invention to reducethis safety risk.

OUTLINE OF THE INVENTION

In one aspect therefore the invention provides a rotary bit with a shankadapted to locate in a chuck, the shank having an insert end and an endsection extending from the insert end, the end section having at leastone elongate flat which locates inside the chuck when the shank isoperatively engaged in the chuck, and a wasted safety section spacedfrom the insert end by a spacing, the spacing of the wasted safetysection from the insert end being sufficient so that when the shank isoperatively engaged in the chuck, the wasted safety section is outsidethe chuck, the wasted safety section having a predetermined shear torquerating so that the shank shears at the wasted safety section if thepredetermined shear torque rating is exceeded.

Preferably, the shear torque rating at which the wasted safety sectionshears is in the range 15-30 ft lbs.

Preferably, the shear torque rating at which the wasted safety sectionshears is in the range 15-20 ft lbs.

Preferably, the shear torque rating at which the wasted safety sectionshears is in the range 25-30 ft lbs.

Preferably, the shank includes a further flat outboard of the wastedsafety section so that after the wasted safety section has been sheared,if necessary, a user may still use the bit on a temporary basis tocomplete a drilling task.

Preferably, the shank includes circumferentially spaced longitudinallyextending flats which locate inside the chuck when the shank isoperatively engaged in the chuck.

Preferably, the shank includes multiple longitudinally extending flatswhich locate inside the chuck when the shank is operatively engaged inthe chuck.

Preferably, the shank has a regular polygonal section including multiplelongitudinally extending flats which locate inside the chuck when theshank is operatively engaged in the chuck.

Preferably, the shank includes circumferentially spaced longitudinallyextending flats which locate inside the chuck when the shank isoperatively engaged in the chuck and there being matching flats outboardof the wasted safety section so that after the wasted safety section hasbeen sheared, if necessary, a user may still use the bit on a temporarybasis to complete a drilling task.

Preferably, the shank includes multiple longitudinally extending flatswhich locate inside the chuck when the shank is operatively engaged inthe chuck and there being matching flats outboard of the wasted safetysection so that after the wasted safety section has been sheared, ifnecessary, a user may still use the bit on a temporary basis to completea drilling task.

Preferably, the shank has a regular polygonal section including multiplelongitudinally extending flats which locate inside the chuck when theshank is operatively engaged in the chuck and there being matching flatsoutboard of the wasted safety section so that after the wasted safetysection has been sheared, if necessary, a user may still use the bit ona temporary basis to complete a drilling task.

Preferably, the rotary bit is a coded one of a coded set of safety bits,the code being according to the shear torque rating and risk factorassociated with the type of drill being used.

Preferably, the rotary bit is a coded one of a coded set of safety bits,the code of each bit in the set being according to the shear torquerating and risk factor associated with the type of drilling activitybeing undertaken. The shank typically has three, six, nine or twelveflats arranged on the insert end of the shank in order to present asurface with is parallel to each jaw of the three jaw chuck.

The shear torque is typically 15-30 ft lbs. Preferably 15-20 ft lbs fordomestic drills and 20-30 ft lbs for industrial drills.

When six, nine or twelve flats are present, the flats may be contiguous.When three flats are provided these may be mutually separated by arcuateportions of the shank in order to retain a substantial proportion of thesection of the shank for taking the rotational force of the chuck. Theflats and the arcuate separation of the flats may be of substantiallyequal sectors.

The flats may be machined, ground, or formed during manufacture.

Theoretically the best resistance to slippage occurs when there is aflat which mates with a closing jaw. Friction is independent of contactarea and depends only upon the closing force and the coefficient offriction between the jaw and the shank. The shank is normally polishedand therefore prone to slip, but the displacement of the jaw must occurbefore the shank can slip. Once flats have been provided on the shankphysical displacement of the jaw is prevented. This ensures that chuckand shank rotate at the same speed rather than reliance upon friction.

Twelve seems to be the upper limit because a greater number begins toapproximate to a circular section which is the cause of the slippage.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the invention are now described with reference tothe accompanying drawings in which:

FIG. 1 is an end view of a partially open chuck;

FIG. 2 is a larger scale section of a shank with six flats;

FIG. 3 is a section of a shank with three flats;

FIG. 4 is a section showing a shear off safety feature applicable to thepresent invention; and

FIG. 5 is a graphical representation of torque in foot pounds againstshear width in millimetres showing a range of widths suited to differentapplications.

METHOD OF PERFORMANCE

Referring to FIG. 1 the three jaws 2 define a triangular space 4 intowhich the shank of a twist drill is inserted. In FIG. 2 the flats 6 areground in the insert end of an HSS shank 8 held in a tool head 10 whichindexes. The flats produce a shank of hexagonal section.

In FIG. 3 the flats 6 are ground on three equi-spaced sectors of theshank diameter. The arc 12 between the flats are equal in distance tothe width of the flats.

The drill includes a shear off safety feature. An example is shown inFIG. 4 at 20 where the flats 21 as previously described are connected tothe bit 22 via a wasted section 23 so that upon jamming of the bit in aworkpiece the wasted section will twist and shear off releasing theoperator. It will be appreciated that the shank of the bit is made longenough that even if it is sheared there is still enough shank so thatthe drill may still be used to complete a drilling procedure if this berequired. However this would not be the safest approach.

Applicant envisages torque safety settings dependent upon the level ofskill or strength of an operator, the nature of the driving tool and thetype of use. For example, household use might be divided into home useor handyman use, industrial use might be divided into light industrialand heavy industrial. The risks involved will vary and hence the torquesafety level will vary as well.

FIG. 5 shows the preferred torque settings for different applications,the shaded region from 15 ft lb torque to 20 ft lb torque is typical fora domestic hand drill whereas the 25 ft lb torque to 30 ft lb torque ispreferred for larger industrial drills in industrial applications. The“jobber” bit is a lower quality steel than the HSS which refers to “highspeed steel” rated bits. Consequently for most applications the wastedsection will be between 5 mm and 7 mm. Having said this it is preferredthat drill bits be colour coded in sets and a recommended coded drillbits for different applications so that the operator may know the safestdrill bit for the particular application. For example, it may bedesirable to select a lower shear width for situations where theoperator is involved with overhead drilling as opposed to a more stabledrilling position where the risk factor associated with a drill beingjammed is less due to greater control of the drill is less awkwardsituations. Applicant recommends a safety rating of 20%-30% lower sheartorque for overhead drilling than for horizontal applications. Thus foroverhead applications in an industrial drill the code would be at thelower end of graph FIG. 5.

In terms of FIG. 5, the lowest torque setting could be 5 ft lbs for ahand held drill set that might be used occasionally by an inexperienceduser. The upper level may be as high as 40 ft lbs in cases such as adrill press where risk of movement of the workpiece being drilled is thehigher. On the other hand wrist injuries might be the higher risk forhand held pistol grip drills and a lower setting would apply. Thus, foursets of drill bits may be purchased, these may be coded by a colouredfiller in the wasted section. Yellow might correspond to generalhousehold and have the lowest torque setting, green to home handyman,blue to light industrial and red to heavy industrial and so on as thetorque setting increases.

Whilst the above has been given by way of illustrative example of thepresent invention many variations and modifications thereto will beapparent to those skilled in the art without departing from the broadambit and scope of the invention as set out in the appended claims.

1. A rotary bit with a shank adapted to locate in a chuck, the shankhaving an insert end and an end section extending from the insert end,the end section having at least one elongate flat which locates insidethe chuck when the shank is operatively engaged in the chuck, and awasted safety section spaced from the insert end by a spacing, thespacing of the wasted safety section from the insert end beingsufficient so that when the shank is operatively engaged in the chuck,the wasted safety section is outside the chuck, the wasted safetysection having a predetermined shear torque rating so that the shankshears at the wasted safety section if the predetermined shear torquerating is exceeded, wherein the shank includes a further flat outboardof the wasted safety section so that after the wasted safety section hasbeen sheared, if necessary, a user may still use the bit on a temporarybasis to complete a drilling task.
 2. A rotary bit according to claim 1wherein the shear torque rating at which the wasted safety sectionshears is in the range 15-30 ft Ibs.
 3. A rotary bit according to claim1 wherein the shear torque rating at which the wasted safety sectionshears is in the range 15-20 ft bs.
 4. A rotary bit according to claim 1wherein the shear torque rating at which the wasted safety sectionshears is in the range 25-30 ft Ibs.
 5. (canceled)
 6. A rotary bitaccording to claim 1 wherein the shank includes circumferentially spacedlongitudinally extending flats which locate inside the chuck when theshank is operatively engaged in the chuck.
 7. A rotary bit according toclaim 1 wherein the shank includes multiple longitudinally extendingflats which locate inside the chuck when the shank is operativelyengaged in the chuck.
 8. A rotary bit according to claim 1 wherein theshank has a regular polygonal section including multiple longitudinallyextending flats which locate inside the chuck when the shank isoperatively engaged in the chuck.
 9. A rotary bit according to claim 1wherein the shank includes circumferentially spaced longitudinallyextending flats which locate inside the chuck when the shank isoperatively engaged in the chuck and there being matching flats outboardof the wasted safety section so that after the wasted safety section hasbeen sheared, if necessary, a user may still use the bit on a temporarybasis to complete a drilling task.
 10. A rotary bit according to claim 1wherein the shank includes multiple longitudinally extending flats whichlocate inside the chuck when the shank is operatively engaged in thechuck and there being matching flats outboard of the wasted safetysection so that after the wasted safety section has been sheared, ifnecessary, a user may still use the bit on a temporary basis to completea drilling task.
 11. A rotary bit according to claim 1 wherein the shankhas a regular polygonal section including multiple longitudinallyextending flats which locate inside the chuck when the shank isoperatively engaged in the chuck and there being matching flats outboardof the wasted safety section so that after the wasted safety section hasbeen sheared, if necessary, a user may still use the bit on a temporarybasis to complete a drilling task.
 12. A rotary bit according to claim 1wherein the rotary bit is a coded one of a coded set of safety bits, thecode being according to the shear torque rating and risk factorassociated with the type of drill being used.
 13. A rotary bit accordingto claim 1 wherein the rotary bit is a coded one of a coded set ofsafety bits, the code of each bit in the set being according to theshear torque rating and risk factor associated with the type of drillingactivity being undertaken.
 14. A rotary bit according to claim 1 whereinthe shank includes circumferentially spaced longitudinally extendingflats which locate inside the chuck when the shank is operativelyengaged in the chuck and the shear torque rating at which the wastedsafety section shears is in the range 15-30 ft bs.
 15. A rotary bitaccording to claim 1 wherein the shank includes multiple longitudinallyextending flats which locate inside the chuck when the shank isoperatively engaged in the chuck and the shear torque rating at whichthe wasted safety section shears is in the range 15-30 ft Ibs.
 16. Arotary bit according to claim 1 wherein the shank has a regularpolygonal section including multiple longitudinally extending flatswhich locate inside the chuck when the shank is operatively engaged inthe chuck and the shear torque rating at which the wasted safety sectionshears is in the range 15-30 ft Ibs.
 17. A rotary bit according to claim1 wherein the rotary bit is a coded one of a coded set of safety bits,the code being according to the shear torque rating and risk factorassociated with the type of drill being used and the shear torque ratingat which the wasted safety section shears is in the range 15-30 ft bs.18. A rotary bit according to claim 1 wherein the rotary bit is a codedone of a coded set of safety bits, the code of each bit in the set beingaccording to the shear torque rating and risk factor associated with thetype of drilling activity being undertaken and the shear torque ratingat which the wasted safety section shears is in the range 15-30 ft bs.19. A rotary bit according to claim 1 wherein the shank includescircumferentially spaced longitudinally extending flats which locateinside the chuck when the shank is operatively engaged in the chuck andthe shear torque rating at which the wasted safety section shears is inthe range 25-30 ft Ibs.
 20. A rotary bit according to claim 1 whereinthe shank includes multiple longitudinally extending flats which locateinside the chuck when the shank is operatively engaged in the chuck andthe shear torque rating at which the wasted safety section shears is inthe range 25-30 ft Ibs.
 21. A rotary bit according to claim 1 whereinthe shank has a regular polygonal section including multiplelongitudinally extending flats which locate inside the chuck when theshank is operatively engaged in the chuck and the shear torque rating atwhich the wasted safety section shears is in the range 15-30 ft Ibs. 22.A rotary bit according to claim 1 wherein the rotary bit is a coded oneof a coded set of safety bits, the code being according to the sheartorque rating and risk factor associated with the type of drill beingused and the shear torque rating at which the wasted safety sectionshears is in the range 25-30 ft Ibs.
 23. A rotary bit according to claim1 wherein the rotary bit is a coded one of a coded set of safety bits,the code of each bit in the set being according to the shear torquerating and risk factor associated with the type of drilling activitybeing undertaken and the shear torque rating at which the wasted safetysection shears is in the range 25-30 ft Ibs.
 24. A rotary bit accordingto claim 1 wherein the shank includes circumferentially spacedlongitudinally extending flats which locate inside the chuck when theshank is operatively engaged in the chuck and the shear torque rating atwhich the wasted safety section shears is in the range 15-20 ft (bs. 25.A rotary bit according to claim 1 wherein the shank includes multiplelongitudinally extending flats which locate inside the chuck when theshank is operatively engaged in the chuck and the shear torque rating atwhich the wasted safety section shears is in the range 15-20 ft Ibs. 26.A rotary bit according to claim 1 wherein the shank has a regularpolygonal section including multiple longitudinally extending flatswhich locate inside the chuck when the shank is operatively engaged inthe chuck and the shear torque rating at which the wasted safety sectionshears is in the range 15-20 ft bs.
 27. A rotary bit according to claim1 wherein the rotary bit is a coded one of a coded set of safety bits,the code being according to the shear torque rating and risk factorassociated with the type of drill being used and the shear torque ratingat which the wasted safety section shears is in the range 15-20 ft Ibs.28. A rotary bit according to claim 1 wherein the rotary bit is a codedone of a coded set of safety bits, the code of each bit in the set beingaccording to the shear torque rating and risk factor associated with thetype of drilling activity being undertaken and the shear torque ratingat which the wasted safety section shears is in the range 15-20 ft Ibs.29. A rotary bit according to claim 1 wherein the shear torque rating atwhich the wasted safety section shears is in the range 5-40 ft bs.
 30. Arotary bit according to claim 1 wherein the shank includes multiplelongitudinally extending flats which locate inside the chuck when theshank is operatively engaged in the chuck and the shear torque rating atwhich the wasted safety section shears is in the range 5-40 ft bs.
 31. Arotary bit according to claim 1 wherein the shank has a regularpolygonal section including multiple longitudinally extending flatswhich locate inside the chuck when the shank is operatively engaged inthe chuck and the shear torque rating at which the wasted safety sectionshears is in the range 5-40 ft Ibs.
 32. A rotary bit according to claim1 wherein the rotary bit is a coded one of a coded set of safety bits,the code being according to the shear torque rating and risk factorassociated with the type of drill being used and the shear torque ratingat which the wasted safety section shears is in the range 5-40 ft bs.33. A rotary bit according to claim 1 wherein the shank has a regularpolygonal section including multiple longitudinally extending flatswhich locate inside the chuck when the shank is operatively engaged inthe chuck and the shear torque rating at which the wasted safety sectionshears is in the range 5-40 ft bs.